Human growth hormone was found to be a mixture of at least five different proteins. The proteins were of three types: a. structural variants of the 191 amino acid form, b. enzymically modified forms where 6-15 amino acids have been removed, c. fragments with molecular weights of 15,000 and less. The various forms are being studied with regard to their growth promoting and hyperglycemic activities, immunological properties and ability to bind to growth hormone receptors. Sequence analysis is being used to determine how the forms differ from the major form of human growth hormone.